More Success With Gene Therapy for Blindness

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WEDNESDAY,
Feb. 8, 2012 (HealthDay News) — As a child, Tami
Morehouse had vision problems.
She struggled to read the blackboard at school, and homework took hours.

Yet, she made it through
high school and college, and became a social worker. Although she was never
able to drive, she learned to ride a bike.

But in her 30s, with three
young children, her vision took a turn for the worse. "I'd be reading a
book and the words faded away," she said.

Morehouse was going blind,
the result of Leber congenital amaurosis (LCA), a rare inherited eye disease
that causes a progressive loss
of vision. "As my kids needed me more and more, I was able to do
less and less," Morehouse said.

That changed in 2009, when
she was one of 12 people to undergo an experimental treatment using gene
therapy in one eye. Now, scientists report even more progress, having
successfully treated the second eye of three patients, including Morehouse. The
new results are published Feb. 8 in Science Translational Medicine.

LCA
is caused by a faulty gene, RPE65, that fails to produce an enzyme needed by
the retina, the tissue in the back of the eye that converts light images into
nerve signals that get sent to the brain.

Lack of the enzyme causes
toxic byproducts to build up in the retinal cells, gradually killing them.

"It's inevitable and
progressive, and people watch as they are losing more and more of their
vision," said Dr. Jean Bennett, an ophthalmology professor at University
of Pennsylvania Perelman School of Medicine and co-leader of the research team
that pioneered the treatment. "By the time they're teenagers or young
adults, they are severely impaired."

The treatment involved
injecting a virus genetically engineered to carry a normal version of gene
RPE65 into the retinal cells.

About two weeks later, with
the eyes now producing the enzyme, the patients — adults and children
— saw a marked improvement in their vision.

"They all gained
vision in a very meaningful way," said Bennett, also a scientist at
Children's Hospital of Philadelphia. "Children can read books, ride their
bikes to their friends' houses — things which they never could do
before."

Initially, researchers only
injected one eye because of safety concerns, Bennett explained. The fear was
that the first injection would prime the immune system to recognize the virus
and attack it when it was injected into the second eye. That would cause
inflammation in the eye, potentially leading to more vision loss.

But animal studies showed
that didn't happen, and so they decided it was safe to try the second eye in
adults.

"It's amazing,"
Morehouse said. "I just feel so different. I used to wake up in the
morning, so afraid and so anxious, that I would look over at the alarm clock
and see nothing."

Prior to the treatments,
she could see light and dark, but most of the world was hazy and gray. By night
time, when her eyes were tired, she could see very little.

Today, her vision is still
significantly impaired. She needs help finding her way to a table in a
restaurant, for example, and reading isn't really possible. Yet, she can tell
when someone is approaching, and she can make out a smile.

"Seeing my daughter
walk across the basketball court. Seeing my son step up to the plate when he's
playing ball — it's phenomenal," Morehouse said.

Researchers verified that
patients could see more by performing functional
MRI scans before and after the second eye treatment. The brain
imaging showed much more response to visual stimuli after their second eye was
done.

At 47, Morehouse was the
oldest patient. The prior study taught researchers that children improved the
most, probably because their retinal cells had suffered less damage.

Now that researchers have
established the procedure is safe in adults, they've started using gene therapy
on the second eyes of children with the condition, Bennett said.

Though more research needs
to be done and there are "technical" issues to be overcome, "we
want to be able to use this approach in developing similar treatments for other
more common blinding diseases," she said.

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